ffmpeg hangs when using -fflags +genpts

I'm trying to remux a .vob file (which I got using vobcopy) into a mp4 container (mkv would do it as well) using ffmpeg 4.2.4-ubuntu0.1. Initially the remuxing finished, but I got these errors:

[mp4 @ 0x560f9a37e5c0] Timestamps are unset in a packet for stream 0. This is deprecated and will stop working in the future. Fix your code to set the timestamps properly

and several thousand times

[mp4 @ 0x560f9a37e5c0] pts has no value

So I tried fixing it using -fflags +genpts:

ffmpeg -fflags +genpts -i 'video.vob' -c copy 'video.mp4'

After processing around 90000 frames ffmpeg gets somehow stuck (but the CPU keeps running on 100%) and can only terminated using kill combined with Ctrl+C.

I tried it with an other .vob file and ffmpeg hanged this time at an other point.

When creating the full debug log I noticed that after the program was aborted the output always shows the same last edited frame (92775). Here you can view it:

1 Answer

I fixed the problem by adding the +igndts flag:

ffmpeg -fflags +genpts+igndts -i 'video.vob' -c copy 'video.mp4'

It resulted in some error messages at the point where ffmpeg hung up earlier, but the created video file was fine.

[mp4 @ 0x56482f355a00] Invalid DTS: 333993600 PTS: 0 in output stream 0:0, replacing by guess
[mp4 @ 0x56482f355a00] Non-monotonous DTS in output stream 0:0; previous: 334018800, current: 334018800; changing to 334018801. This may result in incorrect timestamps in the output file.

I'm not sure what caused the problem and what +igndts does to fix it, but I'm happy that it works.